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SB 608 

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CIRCULAR NO. 170 MAY, 1931 

UNITED STATES DEPARTMENT OF AGRICULTURE 
" WASHINGTON, D. C. 




THE DUTCH ELM DISEASE 

By C'ujnrs IMay, Associate Pathologist, Department of Botany, Ohio Agricultural 
Experiment StaPicn, and G. F. Gravatt', Senior Patholoffut, Division of Forest 
I'iith'tlOiiy, Bureau of Plant Industry, United^ States Department of Agriculture 



CONTENTS 



Page 

Introductiou 1 

Importanre of elms in America 1 

Distrihution of the disease 1 

Susceptible species 2 

Symptoms 5 



Means of spread 5 

The causal organism 7 

Confusing elm troubles 7 

Eradication 9 

Appeal for specimens 9 



INTRODUCTION 

The Dutch elm disease, caused b}' the fungus Graphiu7)i ulmi 
Schwa rz, was discovered in the United States for the first time 
during the summer of 1930. Its presence seriously threatens the 
futui-e of one of our valuable shade and forest trees. The purpose 
of this circular is to interest sliade-tree owners, nurserymen, tree 
surgeons, foresters, and others working with trees in sending in 
specimens from unhealthy elms so that the disti-ibution of the disease 
may be ascertained at once as a basis for control policies. 

IMPORTANCE OF ELMS IN AMERICA 

The American elm {Ul/iius americana L.) is one of our most im- 
portant shade and ornamental species. It is extensively planted 
in this country from coast to coast and from Canada to Mexico. 
In New England this tree gives a distinctive character to the streets 
and parks. Other species of elms are used also as ornamentals in 
various parts of the country. 

In forests elms are important in mixed hardwood stands from the 
Great Plains area to the Atlantic Ocean. The six States leading 
in the production of elm lumber are Wisconsin, Michigan, Indiana, 
Tennessee, Arkansas, and Louisiana. 

DISTRIBUTION OF THE DISEASE 

The Dutch elm disease, wdiich was first noticed in the Netherlands 
in 1919, has caused the destruction of many elms in that country. 
There is as yet no indication of any decrease in its virulence. It 
quickly spread to Belgium, Germany, and France, where in many 
localities it is likewise causing widespread death of elms, (Fig. 1.) 
In Great Britain the first case w^as found in 1927, and now tlie dis- 

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2 CIRCULAR 17 0, V. S. DEPARTMENT OF AGRICULTURE 

ease is reported as prevalent in the southern part of the island. It 
has already spread into Norway, with a cool climate, and into 
northern Italy, with a warm climate, which indicates that the 
disease flourishes under widely different conditions of temperature. 

In the summer of 1930 this disease was identified as present in 
America independently by Christine Buisman, a Dutch plant pathol- 
ogist then traveling here, and the senior writer. Three infected 
trees were found in different parts of Cleveland (fig. 2) and one in 
Cincinnati, Ohio. None of the infected trees came from nurseries, 
and there is at present no satisfactory explanation for the presence 
of the disease in these two localities. 

The native home of the causal fungus is not known. The disease 
is called the Dutch elm disease because it was first noticed in the 




Figure 1. — Lamp elm trees at Versailles. Frame, in various stages of dying from 
the Dutch elm disease in July, 1030. (Photograph by K. Kent Beattie) 

Netherlands, whence it spread to other European countries. It is 
possible that the fungus may be a native of Asia, or even of North 
America. However, this latter source seems highly improbable. 
The American elm is markedly susceptible to the disease, and, al- 
though for a number of years plant pathologists and tree workers 
in the United States have known of its seriousness in Europe and 
have been watching for it here, thus far only the above-mentioned 
four affected trees have been discovered. 



SUSCEPTIBLE SPECIES 

The Dutch elm disease is most prevalent on trees 15 to 40 years old, 
but in Europe both nursery seedlings and large mature trees have 
been found infected. In Europe nearly all species and varieties of 
elm that are grown extensively and that have been exposed to the 
disease appear to be susceptible. The considerable variation re- 
ported in the susceptibility of individual trees or strains within a 
species may account for some differences of opinion regarding the 
relative susceptibility of certain species and varieties. 






THE DUTCH ELM DISEASE 




Figure 2. — One of the wilted American elms which was attacl^ed by the Dutch 
elm-disease fungus in Cleveland, Ohio. The tree first showed wilted parts in May, 
according to the report of the owner; and by the middle of July, when it was 
removed and burned, most of the tree had wilted, and many of the leaves had 
dropped. The tree had discolored streaks in the roots as well as in the trunk 
and twigs 



4 CIRCULAR 17 0, U. S. DEPARTMENT OF AGRICULTURE 

The American elm, which is of most interest in this country, has 
been found to be severely attacked in both England and Germany. 
Inoculations on young trees, made by the senior writer under 
quarantine conditions, as well as those of European investigators, 
confirm its high susceptibility. (Fig. 3.) 




Fif^UEE 3. — On the right is a young American elm 14 days after it was inoculated 
with the Dutch elm-disease fungus. The seedling in the center is one of the 
check trees, which were treated similarly except that the fungus was not Inserted 
In the wound. - The check tree on the left was almost completely severed, hut it 
showed no signs of wilting 

The English elm {Ulmus ccunpestris) , the Holland elm {U. 
hoUandica) , and the Scotch elm {U. glabra), which are planted to 
some extent as ornamentals in this country, are likewise susceptible 
to the disease. ZeK'ova keall, a tree closely related to the elms, also 
has been found by inoculation to be susceptible. 



THE DUTCH ELM DISEASE O 

SYMPTOMS 

ITsiially the first symptom of the Dutch elm disease is the sudden 
wilting of the leaves of a part of the crown of the tree, of the entire 
tree, or of the tips of some of the side branches. Drying of the 
leaves and defoliation of the aifected parts may follow. The wilted 
leaves often turn yellow or brown before falling, and the affected 
parts stand out in color contrast with the rest of the tree. At times 
the wilted leaves remain green and crisp and cling to the tAvigs. 
The one or two end leaves frequently persist longer than the others, 
and the tips of the twigs bend, giving a characteristic appearance, 
which may be of value in detecting affected trees in winter. At 
Cleveland wilting appeared on all three of the trees in the latter part 
of IVIay, but in England the trouble rarely is evident until June and 
frequently not until July or August. The progress of the disease 
on individual trees varies. One limb may wilt one year and others 
in succeeding years, or the whole tree may die in a single season. 
In all three of the cases in Cleveland the first wilting was followed 
in the same season by that of additional parts of the trees. 

On some affected trees the twig growth is short, the leaves fail 
to reach normal size, and the foliage is thin. Often infected trees 
produce luimerous suckers along the trunk and at the bases of the 
large branches. These new shoots may turn brown, or the leaves 
may remain green throughout the season. Suckering, however, is 
not a specific symptom confined to the Dutch elm disease. Trees 
affected Avith this disease may die at the end of the first season or 
may persist for some years. 

If a clean cut is made across a twig affected with the Dutch elm 
disease, a brownish discoloration Avill be seen in the sapwood. (Figs, 
-ir and 5.) In general the discolored tissue does not form a com- 
pletely closed circle but is made up rather of numerous small brown 
dots. Sometimes, however, a contiu-uous ring is formed. The dis- 
coloration may appear in one or more annual rings. If the bark is 
peeled away and the sapwood exjDOsed, the discoloration is evident as 
a series of short, brown streaks. A single streak does not extend 
for a long distance down the twig. In late summer it is sometimes 
necessary to cut away some of the summer wood to find the short 
sti])pled streaks in the spring Avood. 

MEANS OF SPREAD 

Our knoAvledge of this disease is as yet based primarily on 
European publications. luA^estigators there haA^e found that elm 
trees readily become infected with the fungus through wounds on 
buds, tAvigs, limbs, trunks, or roots. Natural infections usually take 
place in the upper portion of the tree. Since the fungus groAA^s 
princi])ally in the sapAvood, which is usually inclosed by a layer of 
healthy bark, outside spore production is supposed to be very slight 
until after the tree or some part of it is killed. Ea^cu then spore 
production on the outer surface is uncommon Avhen compared, for 
instance, Avith the enormous spore production of the fungus causing 
the chestnut blight. Under A^ery favorable conditions spores may 
be produced on cut surfaces of the tree, stumps, chips, tAvigs, and 
in insect tunnels in the wood. Spores are probably produced in 



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CIRCULAR 17 0, U. S. DEPARTMENT OF AGRICULTURE 



insect tunnels much more frequently than on exterior surfaces. The 
fungus has been found in leafstalks, but as yet no information is 
available as to the importance of leaves in the dissemination of the 
disease. 

In Europe the spread of the disease from tree to tree is now con- 
sidered to be primarily by means of an elm-bark beetle {Scolytus 
scolytus Fabr.) which carries the fungus on its body and which 
makes wounds in different parts of the tree, thus giving the fungus 
a chance to secure entrance. This particular elm beetle has not 
been found in America, but it is feared that some of our native 




Figure 4. — Sections from a diseased limb, showing tlie discolored areas or 
streaiis in the sapwood 

elm insects may prove to be carriers, because in Europe the spores 
have been found on the bodies of insects other than this bark beetle. 
Although the Dutch elm disease is not prevalent in nurseries in 
Europe, it is known to occur in them at times. Therefore, nursery 
stock is a possible means of spread, especially for long distances. 
Since June 1, 1919, the importation of elm nursery stock into the 
ITnited States has been under special permit only and has been 
limited to such material as is necessary for the purpose of keeping 
the country supplied with new varieties and necessary propagating 
stock or for any necessary experimental, educational, or scientific 



THE DUTCH ELM DISEASE 



purpose; and since the seriousness of the Dutch ehn disease in 
Europe has been realized, no sucli permits even have been issued. 
No imported ehns have been known to come to the Ohio region from 
Europe since tlie disease was discovered in the Xetherhmds. 

THE CAUSAL ORGANISM 

Graflimm uhni^ the fungus causing the 
Dutch elm disease, is closely related to 
some of the organisms that produce blue 
stains in the wood of pine, gum, and other 
trees. In from three to seven days the 
fungus grows out from small pieces of 
diseased sapwood planted in potato-dextrose 
agar. The growth generally has a slimy 
appearance. In the writers' cultures con- 
centric zones were formed in all the original 
isolations; but after the fungus had been 
in culture for some time a greater amount 
of aerial mycelium developed in the sub- 
cultures, and the zonation became indistinct. 

Young cultures form spores acrogenously 
and in great abundance. The numerous glis- 
tening spore heads or clumps of various sizes 
show up very clearly under the low power 
of the microscope. In the writers' cultures 
the spores range from 3 by 1.5 microns to 7 
by 4 microns. The spores are generally 
more or less pear shaped, but also vary con- 
siderably in this respect. Yeastlike budding 
of the spores is commonly found in the cul- 
tures, and on some media the culture itself 
looks like a yeast colony. 

The Cephalosporiumlike stage of the 
fungus usually is followed in a few days 
by the coremial stage. The coremium is 
a spore-bearing structure made up of a 
black stalk, lighter colored at the top, and 
surmounted by a subspherical ball of spores. 
These spores are hyaline and average about 
3.2 by 1.7 microns. The stalks may be up 
to 1,200 microns long by 120 microns thick. 

These coremia grow up both from the 
bits of diseased wood used for the isolations 
and from the agar itself. The production 
of coremia by the fungiis is somewhat ^'ea'sed fim'^^ith'most of the 
erratic, and most of the w^riters' subcultures bark removed to show the 

1 1 • xi • J. short dark streaks iii the 

are no longer producing this stage. sapwood 




CONFUSING ELM TROUBLES 



At present it is often impossible to state from a field examination 
whether a wilted elm has or has not the Dutch elm disease. Even 
the presence of the characteristic streaks in the. sap wood does not 
make field diagnosis positive, since some other fungi and bacteria 



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CIDCULAR 170, U. S. DEPARTMENT OF AGRICULTURE 



cause similar types of wood discoloration. Most of the organisms 
cultured from discolored sapwood are regarded as weak parasites; 
that is, organisms that are making growth in the living sapwood only 
because the tree has been weakened. Trees injured by soil fillings, 
drought, illuminating gas, insects, etc., are invaded by fungi Avhich 
help to hasten the death of some part or the whole of the tree. 
Graphium also invades weakened trees, but in Europe it differs from 
l^arasites of low virulence in being able by itself to bring about the 
death of vigorously growing trees. 

Except by laboratory cultures, it is usually impossible to dis- 
tinguish elms attacked by the fungus causing the Dutch elm dis- 




FiGUEE 6. — An American elm attacked by Vertieillium. 
The sross symptoms are very similar to tho.se of the 
Dutch elm disease 

ease from those attacked by the fungus group Vertieillium (fig. 6), 
which causes the wilt of maples and a number of other trees and 
shi-ubs and many herbaceous plants and which is an active parasite 
growing in the living sapwood of the tree. As many of the external 
symptoms of the two diseases are similar and as only a few trees 
affected by them in this country have been studied, it is inadvisable 
to attempt to distinguish them in the field. However, the discolora- 
tion of the sapwood is somewhat more continuous with the Vertieil- 
lium wilt than with the Dutch elm disease. In the Vertieillium wilt 
of small nursery trees of maple and elm, and in some of the large 
planted trees, the disease starts in the roots and grows upward. 



THE DUTCH ELM DISEASE 9 

In the Dutch elm disease infection through the root under natural 
conditions has never been reported. In one case in Cleveland, cul- 
tures showed that Graphium and Verticillium were both present 
in the same tree. 

The twig blight of the elm, caused by the fungus Sphaeropsis 
vJmicola., is widely distributed in this country. Individual twigs 
or many twigs over a tree may be killed by it, and the continuation 
of the attack often results in the death of the tree. This disease 
seems to be more serious under Wisconsin climatic conditions than 
imder those of the Eastern States. Affected twigs usually show 
definitely cankered and killed areas in the bark, accompanied by 
short, continuous, darkened areas in the wood. On the other hand, 
a recently wilted ' branch or twig from a tree affected only by 
Graphium or Verticillium will have normal green bark without 
cankers and numerous discolored streaks in the sapwood. 

For a number of years there has been an extensive dying of the 
elms in parts of the Ohio and upper Mississippi River Valleys. The 
underljdng cause of this dying is not known, though various fungi 
of a parasitic nature have been found on the affected trees. The 
external symptoms in some cases resemble those of the Dutch elm 
disease, but in most cases the streaks and spotting in the sapwood 
characteristic of that disease are absent. 

ERADICATION 

No cure is known for a tree affected with the Dutch elm disease 
unless the infection is entirely localized in a branch that can be 
completely removed. Since ap})arently the disease is as yet in an 
incipient state in the United States, the only logical program involves 
the location and the eradication of all infected trees. In Europe 
the disease is widespread and such eradication would not be feasible. 
Data on many phases of this disease are still lacking, but enough is 
know]i to justify aggressive action at the present time. Delayed 
action may result in the loss of the opportunity to eradicate the 
disease from this country. 

To eradicate a tree affected Avith the Dutch elm disease, remove 
and burn all parts except the deeper roots. Those roots remaining 
should be covered with 6 inches or more of soil. Burn all chips 
and pieces of bark. Pick up and burn the leaves. Treat the tools 
used Avith denatured alcohol or f-ome other active disinfectant. 

APPEAL FOR SPECIMENS 

Available Government funds are merely sufficient to do the 
necessary cultural work on specimens, to make some research studies, 
and to conduct inspection around know^n infections. State pathol- 
ogists, foresters, and State departments of agriculture in the impor- 
tant States are fully alive to the danger from this disease and are 
cooperating in the survey now being made. But the cooperation of 
tree workers and owners in locating and sending in twig and branch 
specimens from elm trees suspected of being infected with the Dutch 
elm disease is also necessary. The territory over Avliich the elm 
growls is so extensive that the only possible way of securing an 
estimate of present conditions is through widespread cooperation. 



10 CIRCULAR 17 0, U. S. DEPARTMENT OF AGRICULTURE 

The best specimens for laboratory culture work are twigs and small 
branches from one-quarter to 1 inch in diameter and from 5 to 10 
inches in length. They should be taken preferably from a part of 
the tree that has recently wilted or died or that has small, under- 
sized leaves, rather than from parts that have been dead for many 
months. Several such pieces should be securely wrapped in paper 
and mailed to the Dutch Elm Disease Laboratory, Agricultural Ex- 
periment Station, Wooster, Ohio, or to your State plant pathologist, 
together with a letter giving the location of the tree and its symptoms. 
The package should bear the name of the sender, and if specimens 
are from more than one tree, each should be numbered or other- 
wise designated. The specimens will be cultured and the cause of the 
disease determined at the Dutch Elm Disease Laboratory, which is 
cooperatively maintained by the Bureau of Plant Industry and the 
Ohio Agricultural Experiment Station. This laboratory will receive 
material from all parts of the United States and is not limited to 
that from Ohio. Information regarding the results of the cultures 
will be sent to each collector. 

While at the present time it is perhaps more probable that the 
Dutch elm disease may be found in ornamental rather than in forest 
trees, still the cooperation of foresters in the search for it is earnestly 
requested. This disease has spread to the forests in Europe, and the 
elm forests of this country must be watched. In addition to diseased 
twigs, pieces of stained elm logs and lumber are desired. 



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